The present invention is related to an antenna, and more particularly to an antenna adapted to operate in more than one frequency band.
With the increased use of wireless communication devices, available spectrum to carry communication signals is becoming limited. In many cases, network operators providing services on one particular band have had to provide service on a separate band to accommodate its customers. For example, network operators providing service on the Global System of Mobile (GSM) communication system in a 900 MHz frequency band have had to also rely on operating on the Digital Communication System (DCS) at an 1800 MHz frequency band. Accordingly, wireless communication devices, such as cellular radiotelephones, must be able to communicate at both frequencies, or possibly a third frequency spectrum, such as the Personal Communication System (PCS) 1900 MHz or Global Position System (GPS) 1500 MHz.
Such a requirement to operate at two or more frequencies creates a number of problems. For example, the wireless communication device must have an antenna adapted to receive signals on more than one frequency band. Also, as wireless communication devices decrease in size, there is a further need to reduce the size of an antenna associated with the device.
An extendible antenna can be used to advantage to provide multiple frequency operation, but such an antenna poses problems to an end user. Because the antenna will typically perform better when in the extended position, the user is required to extend the antenna before operating the wireless communication device. Users may not regularly do this as the device may usually operate with the antenna in a retracted position, and this action requires extra effort. As a result, many end users prefer a fixed or xe2x80x9cstubbyxe2x80x9d antenna which does not need to be extended during operation. However, the fixed antenna must provide multi-band functionality.
As the need for multi-band operation in radiotelephones increases, a greater demand is placed on the antenna to cover all these frequencies of operation using a small, compact structure. Moreover, antennas need to be efficient with good return loss performance and suitable radiated patterns. Further, antennas are adversely affected by the proximity of a user""s hand, which is almost unavoidable with increasingly small telephone sizes.
Accordingly, there is a need for a small fixed antenna adapted to receive signals in multiple frequency bands. In addition, it would be of benefit if the different resonant elements of the antenna can be commonly driven. It would also be advantageous to provide the antenna structure in a compact, fixed structure that is less susceptible to efficiency changes due to the placement of a user""s hand on or near the antenna.